Would the rocks found in bags in the garden section work in my tank if I boiled them to clean them? I have a few (never used in my garden, or my aquarium, yet) that are pretty nice in size,and they look just the the river rocks sold in the aquarium area (not quite as shiny though). I was wanting to stack them up and make a little cave/tunnel thing for my fish and possibly attach some anubias and moss to it eventually. I am just trying to use some things I already have because I don't have much money at the moment. But, if you think it may harm my fish i won't do it. I am just curious if anyone has ever used them before, and what the difference is?.

Well, you could test the rocks by putting a drop of white vinegar on them. If they fizz, don't use them. But I heard some people say that this test isn't too reliable. The rocks most probably will be safe if it isn't limestone and if there isn't anything metallic in them. It's really a judgment call for you alone. Since we don't know the specific type of rock it is, you can't be too sure whether it is safe or not. All you can do is either not use them or use them and monitor your fish for any signs of change.

If you decide to use them, please make sure NOT to boil them. There can be air pockets in the rocks that when boiling the rocks will cause them to explode. O_o

You can boil water and pour on the rocks to soak. Just want you to be safe :)

If you are going to use rocks for your local garden store or just from your backyard then make sure, like ilovebunnies said, that they aren't limestone or metallic and then before you put them in a tank fill a bucket with hot, not boiling, water and let the rocks sit in that for 24 hours to kill off any parasites. The next day, rinse them thoroughly under warm water until there is no dirt coming off (remember not to use any soaps or chemicals as this can harm your fish) and then they are safe to use.

Well, you could test the rocks by putting a drop of white vinegar on them. If they fizz, don't use them. But I heard some people say that this test isn't too reliable. The rocks most probably will be safe if it isn't limestone and if there isn't anything metallic in them. It's really a judgment call for you alone. Since we don't know the specific type of rock it is, you can't be too sure whether it is safe or not. All you can do is either not use them or use them and monitor your fish for any signs of change.

If you decide to use them, please make sure NOT to boil them. There can be air pockets in the rocks that when boiling the rocks will cause them to explode. O_o

You can boil water and pour on the rocks to soak. Just want you to be safe :)

That is what I meant, pouring the hot water on the rocks and soaking them. Not acutally rapidly boiling them on the stove..just goes to show I need coffee before typing in the morning.

Thanks for the advice you all. I will try and find the bag they came in and see what kind of rock they are. They look almost identical to the river stones sold in smaller bags in the fish department, but they're less shiny.